The objectives of the Center for Gamma-Ray Imaging (CGRI) are to develop advanced gamma-ray detectors and imaging systems, to push the limits of spatial and temporal resolution in SPECT and PET, and to make state-of-the-art technology available to our collaborators and to the biomedical research community. Much of the emphasis is on basic research with animal models, but there are many possibilities for translating the technology and the results of the collaborative research into clinical practice. We strive to integrate the components of the P41 mechanism (core technology development, collaborative research, service, dissemination and training) into a comprehensive program that addresses all aspects of gamma-ray imaging, including the radiopharmaceutical, image formation and detection data acquisition and processing and the final biomedical application. The core technology projects include development of new gamma-ray detectors with high sensitivity and high spatial and temporal resolution; development of new computer models and image reconstruction algorithms for SPECT and PET; design and construction of new imaging systems incorporating sophisticated list-mode data-acquisition electronics; objective task-based assessment of image quality as applied to evaluation and optimization of imaging systems and algorithms; and development of new animal models and image-analysis methods for molecular imaging. Collaborative research includes projects in functional genomics, lymphology, nephrology, oncology and cardiology. Dissemination includes supplying imaging hardware and software to our collaborators, as well as workshops and a web site for traditional dissemination of information. Training includes both a formal workshop and hands-on training for our collaborators in Tucson. Service includes performing routine animal studies, testing and calibrating detectors and detector materials, and providing advice on image quality.